Electrode structure



June 14, 1966 JARASSE ET AL ELECTRODE S TRUCTURE Filed Nov. 7, 1963INVENTORS l-JARASSEe/JJO/fifr BY 7QJQ2. 8M? ATTORN Y United StatesPatent Ofiice 3,256,458 Patented June 14, 1966 7 Claims. a. 313-106) Thepresent invention relates to electrode structures for electron tubes,and more particularly to electrode structures devoid of parasiticthermo-ionic emission for use in electron tubes exposed to hightemperatures.

It is known that when certain electrodes of electronic tubes, eitherdiodes or polyodes, carried during a portion of the operating cycle at anegative potential with respect to the cathode, attain suificienttemperatures, for example, above 300 C., a parasitic phenomenon due tothe thermoionic emission of these electrodes appears disturbing theoperation of the tube in an unacceptable manner.

Objects of the present invention are to provide improved electrodes, inparticular for'tubes subjected to technological treatments at hightemperature, for example of the order of 1,000 C., or which attainelevated temperatures in the operation thereof, in which thisthermoionic parasitic emission is very strongly reduced, if notcompletely suppressed.

One well known means for suppressing thermal emission consists incoating the electrodes with an anti-emissive substance such as gold,platinum or titanium, for example, by way of electrolytic deposit.

Nevertheless, in the known tubes of the prior art, this coating has beenapplied to relatively massive or solid electrodes, with the quantity ofmaterial in the electrolytic deposit being negligible as compared to thequantity of material making up the electrode.

When it is necessary for these tubes to be operated at elevatedtemperatures, or when they are subjected in the course of themanufacture thereof to operative cycles at elevated temperatures, adiffusion of the aforesaid coating into the relatively thick supportmetal occurs. This means that the coating actually disappears by reasonof the negligible ratio of the quantities of materials mentionedhereinabove. The surface then loses its initial anti-emissiveproperties, moreover, the superposition of several layers ofelectrolytic deposits wherein an intermediary serves as a barrierbetween the support and the anti-emissive deposit is only an onerous andlittle effective solution thereto.

According to the present invention, an electrode displaying no parasiticthermo-ionic emission in tubes subjected to high temperautres has beendeveloped and is characterized by the fact that it is supported by aceramic wall and that it is constituted by the combination of a sinteredmetal layer, known for its capacity to form a conductive refractorysurface, and a coating of anti-emissive metal, known per so. In thiscombination, the thicknesses of the coating and of the sintered layerare in a ratio that is not negligible, for example, 1:10.

Since, in accordance with the present invention, the quantity ofmaterial in the coating is no longer negligible with respect to that inthe metal support, the diffusion of a portion of the coating into thesub-adjacent metallized layer does not penetrate any further than thesurface of the ceramic material and leaves a suflicient quantity ofcoating metal remaining on the surface of the sintered layer in order topreserve the anti-emissive properties thereof. Additionally, a fractionof the coating metal enters into combination by way of compoundformation with the constituent elements of the base layer producingultimately a refractory layer that is stable and which possessesanti-emissive properties at high temperatures.

Accordingly, it is an object of the present invention to provide aprocess for the manufacture of an electrode structure which is capableof withstanding high temperatures without losing its anti-emissivequalities and to an electrode structure produced by such a processhaving the desired lasting anti-emissive properties.

Still another object of the present invention resides in the provisionof an electrode structure capable of operating at high temperatureswithout the emission of electrons which is simple, effective, and avoidsthe shortcomings and drawbacks encountered with the prior artstructures.

A further object of the present invention resides in the provision of anelectrode structure capable of retaining its anti-emissivecharacteristics even under high operating temperatures which may bereadily manufactured in an inexpensive manner.

A still further object of the present invention resides in the provisionof an electrode structure of the type described hereinabove which isprovided with an anti-emissive layer that is capable of performing fullysatisfactorily for its intended purposes notwithstanding exposure of theelectrode structure to high temperatures and very high inverse voltages.

These and other objects, features and advantages will become moreobvious from the following description when taken in connection with theaccompanying drawing which shows, for purposes of illustration only, inthe single figure thereof, one embodiment of an electrode structureobtained in accordance with the process of the present invention.

A process for the realization of such an electrode will be describedhereinafter as a non-limiting example, applied to the anode of a veryhigh-voltage diode having a cermaic envelope, intended for operation ina hot surrounding or environment, for example, of 350 C., whereby theanode may attain or exceed 500 C.

An electrode is made by forming a sintered conductive metal layer on aceramic supporting surface, obtained by sintering in a hydrogenatmosphere at 1,550 O, a layer having a molybdenum base, or a molybdenumand titanium base, or a molybdenum, manganese and iron base, etc. Thethickness of the layer thus formed is of some tens of microns.

On this conductive refractory surface there is deposited by electrolyticmeans or any other suitable known way, a substance having the desiredanti-emissive properties such as, for example, gold. The thickness ofthe thusly obtained deposite is of the order of microns.

The ceramic piece thus treated is thereupon reheated under vacuum at ahigh temperature of the order of 1,000" C.

One obtains thereby finally a stable refractory layer wherein thermalemission under inverse voltages of the diode is reduced, and in the caseof operation at anode temperatures of the order of 500 C., asexperiments have indicated, to a ratio of 10- to 10- relative to tubesnot treated in accordance with the present invention.

Referring now to the single figure of the drawing which represents apartial cross sectional view through an electrode structure inaccordance with the present invention, reference numeral 1 designatestherein the sintered layer applied onto a ceramic support 2. Thesintered layer 1 is coated with a deposit of anti-emissive metal 3 andthe assembly thus constituted forms the electrode having no parasiticthermal emission for a tube subjected to high temperatures.

While we have shown and described one embodiment in accordance with thepresent invention, it is understood that the same is not limitedthereto, but is susceptible of numerous changes and modifications withinthe spirit and scope of the present invention as known to a personskilled in the art, and we therefore do not Wish to be limited to thedetails shown and described herein, but intend to cover all such changesand modifications as are encompassed by the scope of the appendedclaims.

We claim:

1. An electrode structure for an electron tube adapted to be exposed tohigh temperatures while retaining its anti-emissive properties,comprising a ceramic support, a sintered layer of a metal having theproperty of forming a conductive refractory surface coating saidsupport, and a layer of a metal coating said refractory surface andhaving the property of substantially suppressing emission of electronsfrom said refractory surface upon heating thereof.

2. The electrode structure of claim 1, wherein said sintered layer isconstituted by metals selected from the group consisting of molybdenum,a combination of molybdenum and titanium and a combination ofmolybdenum, manganese and iron.

3. The electrode structure of claim 1, wherein said layer of a metalcoating said refractory surface is selected from the group consisting ofgold, platinum and titanium.

4. An electrode structure for an electron tube adapted to be exposed tohigh temperatures while retaining its anti-emissive properties,comprising a ceramic support, a sintered layer of a metal having theproperty of forming a conductive refractory surface coating saidsupport, and a layer of a metal coating said refractory surface andhaving the property of substantially suppressing emission of electronsfrom said refractory surface upon heating thereof, the ratio ofthickness of the said respective emis' sion-suppressing and sinteredlayers being about 1:10.

5. An electrode structure for an electron tube adapted to be exposed tohigh temperatures while retaining its anti-emissive properties,comprising a ceramic support, a sintered layer of a metal having theproperty of forming a conductive refractory surface coating saidsupport, and

4, a layer of a metal coating said refractory surface and having theproperty of substantially suppressing emission of electrons from saidrefractory surface upon heating thereof, said ceramic support forming apart of the enclosure of the tube.

6. An electrode structure for an electron tube adapted to be exposed tohigh temperatures while retaining its anti-emissive properties,comprising a ceramic support, a sintered layer of a metal selected fromthe group consisting of molybdenum, titanium, manganese, iron and alloysthereof having the property of forming a conductive refractory surfacecoating said support, and a layer of a metal consisting essentially ofgold coating said refractory surface and having the property ofsubstantially suppressing emission of electrons from said refractorysurface upon heating thereof.

7. An electron tube adapted to be exposed to high temperatures,comprising enclosure means, and an electrode structure retainingits'anti-emissive properties, said electrode structure including aceramic support forming part of said enclosure means, a sintered layerof a metal having the property of forming a conductive refractorysurface coating said support, and a layer of a metal coating saidrefractory surface and having the property of substantially suppressingemission of electrons from said refractory surface at high temperatures.

References Cited by the Examiner UNITED STATES PATENTS 2,497,111 2/ 1950Williams 313-355 X 2,527,513 10/1951 Arditi et a1. 313106 2,576,12911/1951 Levin 313-106 2,647,218 7/ 1953 Sorg et a1 31329l X 2,754,4457/1956 Sorg 313-291 X JOHN W. HUCKERT, Primary Examiner. DAVID J.GALVIN, Examiner.

A. J. JAMES, Assistant Examiner.

6. AN ELECTRODE STRUCTURE FOR AN ELECTRON TUBE ADAPTED TO BE EXPOSED TOHIGH TEMPERATURES WHILE RETAINING ITS ANTI-EMISSIVE PROPERTIES,COMPRISING A CERAMIC SUPPORT, A SINTERED LAYER OF A METAL SELECTED FROMTHE GROUP CONSISTING OF MOLYBDENUM, TITANIUM, MANGANESE, IRON AND ALLOYSTHEREOF HAVING THE PROPERTY OF FORMING A CONDUCTIVE REFRACTORY SURFACECOATING SAID SUPPORT, AND A LAYER OF A METAL CONSISTING ESSENTIALLY OFGOLD COATING SAID REFRACTORY SURFACE AND HAVING THE PROPERTY OFSUBSTANTITLALY SUPPRESSING EMISSION OF ELECTRONS FROM SAID REFRACTORYSURFACE UPON HEATING THEREOF.